1. Field of the Invention
The present invention relates to aircraft flight control devices, and more particularly to wing-mounted control devices. More specifically, the invention relates to an improved aileron system especially suitable for fixed-wing aircraft which provides a flight control system having improved efficiency and versatility.
2. Related Art
Immediately obvious with the invention of the airplane was the importance of controlling movement in flight, as an uncontrollable airborne airplane will soon crash. Aviators soon settled on ailerons for roll control. An aileron is a hinged panel on the trailing edge of the wing, usually located at the outboard portion of the wing, which, when deflected downwardly, increases the lift of that wing, to roll or bank the airplane into a turn. At the same time, the aileron on the other wing is deflected upwardly, to decrease the lift on that wing and thus augment the rolling motion. The configuration and application of the conventional aileron system has changed little, if at all, over more than nine decades since the first fixed-wing aircraft were produced.
One of the most objectionable features of conventional aileron application is a phenomenon known as xe2x80x9cadverse yaw,xe2x80x9d and virtually all existing fixed-wing aircraft suffer disadvantageous consequences associated with adverse yaw. When a turn is initiated with conventional ailerons, the nose of the airplane turns first in a direction opposite to that of the intended turn. This is usually compensated by using rudder deflection to xe2x80x9ccoordinatexe2x80x9d the turn. The adverse yawing motion is a direct result of aileron application. While producing more lift to bank the airplane into a turn, the downwardly-deflected aileron also produces more drag, which acts momentarily to cause the airplane""s nose to turn in the direction opposite to the intended turn. That is, when one wing is lifted relative to the other wing by operation of a conventional aileron to bank the airplane into a turn, it is also pulled back away from the turn relative to the wing on the other side, causing the nose initially to turn, or yaw, in the direction opposite to the turn. This effect becomes increasingly detrimental as the roll rate increases and/or airspeed decreases.
Adverse yaw produced by the conventional aileron contributes to spin entry. Instinctive application of conventional ailerons during attempted spin recovery merely aggravates the spin condition. When spinning, an airplane is descending and turning in a tight spiral flight path. The conventional aileron is not effective in spin recovery. In a left hand spin, for instance, the left wing is down and toward the center of the spiral. Instinctively, many pilots are tempted to initiate right stick or control yoke movement to roll towards the right and out of the spin. With conventional ailerons this will deploy the left aileron down and the right aileron up. The left aileron will create more drag than the form drag caused by the up-going right aileron and the spin will be further aggravated. For an airplane equipped with conventional ailerons application of rudder alone is used for spin recovery. Much of spin training involves conditioning pilots to avoid the instinctive attempt to roll out of the spin. Nonetheless, many pilots have aggravated spins by attempting such recoveries with conventional ailerons.
Various methods and devices have been used to counter adverse yaw. Among them are the differential aileron with its finite deflection ratio, and the spoiler. The differential variation of conventional ailerons is the most commonly used solution and provides some marginal improvement, but has limitations. Use of spoilers may obviate adverse yaw, but spoilers present their own problems. Spoilers are so named because they spoil or effectively eliminate lift. Ailerons deliver continuously variable changes in lift within their operational envelopes, whereas spoilers operate in a stepwise manner, being functionally either on or off, and thus are difficult to modulate between full and zero effect. Roll control is difficult to achieve with spoilers without complicated sub-systems or augmenting devices.
Another disadvantage of conventional ailerons is that they also require commitment of a sizable portion of the trailing edge of the wing that could otherwise be used for beneficial high-lift devices. Such devices allow lower approach, landing and takeoff speeds, especially advantageous for heavy, high-speed commercial and high-performance military aircraft.
There are several prior-art devices which, at first glance, may appear very similar to the present invention. On closer examination, however, none of them yields the stated results or functional capabilities of this invention. Most of the previously employed devices are designed and applied as drag devices, such as ground control spoilers, drag rudders, dive brakes, or nominal flaps.
Examples of devices known in the art which are deployed upwardly to provide aircraft control may be found in the following U.S. patents:
Pouit describes a flap which acts more like a present-day spoiler, to prevent aircraft capsizing. In a variation, the flap has separate upper and lower elements, of which the upper element is simply hinged, and can be extended upwardly only by the upper deflection of the lower, actuated element. The upper flap member is not capable of movement independent of the lower member. Both wing flaps are operated together. Perrin describes a glider control system wherein the aileron has a secondary aileron which can be extended up to act as a drag rudder for directional yaw control in place of a rudder.
Fenton relates to a device which is basically a flap with small, subsidiary flaps on the upper and lower trailing edges. The subsidiary flaps are moved up or down through fixed, predetermined displacement, to control aircraft roll movement, with the deployment of the subsidiary flap on each side of the aircraft controlled such that when the subsidiary flap on one side is up, the corresponding subsidiary flap on the other side is down. Due to their small size, the effectiveness of the subsidiary flaps is doubtful.
Clauser et al. provide a lateral control arrangement having an airfoil member pivoted near the tip of the wing which functions as an aileron and a flap, or an xe2x80x9cailerflap,xe2x80x9d and a second airfoil member, or a xe2x80x9cslot lip,xe2x80x9d pivoted above the ailerflap. Each element can pivot up and down about its neutral position. The slot lip regulates the slot spacing between the wing""s trailing edge and the leading edge of the ailerflap, to alter the lift provided by the ailerflap during takeoff and landing. During flight, lateral control is achieved with the ailerflaps operated conventionally as ailerons. The slot lips move in unison with the ailerflaps, and are not capable of independent upward movement.
Johnson relates to a landing control system having a spoiler located above a conventional flap. The downwardly extending flap is used to augment lift, and the upwardly extending spoiler act as a drag plate during landing approach. The flap and spoiler on both wings are actuated simultaneously.
Miller provides a split aileron which is a combination aileron and flap. Each wing has an aileron extending almost the full span, and a flap pivoted beneath the aileron. The aileron functions conventionally, and size of the flap is limited to that of the aileron. Wright et al. describes a split flap arrangement wherein a lower element pivots down as a flap and an upper element, which pivots up and down, serves as an aileron. Riviere, Taylor and Sepstrup disclose split aileron arrangements.
Other examples of control surfaces which are formed of two, separately hinged sections and can be deployed together up and down as conventional flaps or ailerons, and are also capable of separating from each other to provide flap and air brake functions, are described in U.S. Pat. Nos. 2,427,980, 2,445,833, 2,612,329 and 2,582,348.
More recently flaperons have been employed which function both as flaps and ailerons, and offer pseudo-full-span flaps. They, however, greatly compromise the roll function and produce even greater adverse yaw than the conventional aileron when roll function is needed. Spoilers attempt to achieve objectives similar to those of the present invention, but at a great compromise in flight characteristics. Spoilers tend to have dead bands and are difficult to modulate. They, after all, xe2x80x9cspoilxe2x80x9d rather than modulate lift. Roll control systems involving spoilers have been used on aircraft with mixed results.
The conventional differential aileron used on most existing aircraft lessens but does not eliminate adverse yaw. It occupies a sizable portion of the wing""s trailing edge, thus preventing the installation of full-span flaps. With some aircraft designs, high roll rates have been sought with the use of full-span ailerons, thus obviating entirely the installation of flaps. Other aircraft designs have sacrificed ailerons for full-span flaps, necessitating the inefficient use of tail planes or wing spoilers for roll control. No other flight control devices have the versatility or efficiency of the present invention. The Frise aileron also claims to lessen adverse yaw by deliberately creating more drag on the upwardly-deflecting aileron. This device also does not allow installation of a full-span flap.
The device closest in construction and function to the present aileron system was invented by the inventors of the present invention. Presented as the xe2x80x9cDelta aileronxe2x80x9d which was placed on top of a one-piece full-span flap, it has some of the features of this invention. But, it is not aerodynamically as efficient and offers less functional capability than the present invention. For example, it does not have an auxiliary flap and in its present form cannot be used as a drag rudder.
The aileron system of the present invention simultaneously eliminates all the above problems while offering desirable features not possessed by conventional ailerons. Accordingly, an object of the invention is to provide an aileron system which is simple in design and construction, and more importantly, in its unique method of deployment and the functional results obtained. Other objects of the invention are to provide an aileron system of the foregoing type which: eliminates adverse yaw associated with previous aileron roll control systems; provides benefits in spin avoidance and spin recovery; can be deployed for flight path control, air braking and as a drag plate; results in a wing which is cleaner, with fewer actuating mechanisms, and is aerodynamically efficient and correct in operation; allows for the incorporation of full-span flaps and other high-lift devices on the trailing edge of a wing; and provides an overall aircraft control system which is simpler in construction and requires fewer components, is less expensive, reduces maintenance requirements, reduces weight, and provides the aircraft with lower takeoff and landing speed capabilities, with the advantages attendant therewith.
The present invention is basically used for roll control of fixed-wing aircraft around the longitudinal axis. It is a combination of aerodynamic control surfaces which deflect upwardly only when deployed for roll control. By operating these surfaces judiciously and in conjunction with their counterparts on the other wing, and the flap systems, many favorable results may be obtained for the control of aircraft.
The aileron system of the present invention is similar in shape and external appearance to the conventional aileron, but its construction and deployment are entirely different. It is comprised of two panels located at the rear portion of the wing, in a spanwise direction and aligned with the wing""s trailing edge. The panels may be independently hinged at their leading edges or may be hinged on a common axis and rotate to make angular deflections with respect to the wing. The upper or aileron panel is deflected upwardly only from the neutral position, while the lower, auxiliary flap is capable of both upward and downward deflections from the neutral position. The upper panel is deployed independently as an aileron and the lower panel is deployed independently as an auxiliary flap. Both panels are deployed together upwardly only as an aileron.
For roll control of an aircraft during cruise, the aileron panel on one side only is deflected up while the aileron panel on the other side remains in its neutral position. The auxiliary flap panel is arranged to move with the aileron panel as a unit, such that the two surfaces form an xe2x80x9caileronxe2x80x9d in the usual sense. To roll left, for example, the aileron of the present invention on the left wing is deflected up, while the aileron on the right wing remains in the neutral position. The upwardly-deflected left aileron results in a negative change in the wing""s lift coefficient, decreasing the lift on the left wing relative to that of the right wing, and producing a roll to the left. Effectively joining the upper and lower panels to move as a unit preserves the smooth contour of the airfoil. In the deflected mode it is the equivalent of an airfoil with a reflex camber. Aerodynamically this is a much more efficient xe2x80x9caileronxe2x80x9d than that achieved by deflecting only the upper panel upwardly.
During flap deployment, the lower auxiliary flap panel is disengaged from the upper aileron panel, and operated to move with the main wing flaps to form a full-span flap. The upper aileron panel is then moved independently to provide roll control. Only the auxiliary flap panel is arranged to move in conjunction with the aileron in the roll control mode. The panel used as a dedicated flap is unaffected.
For use on small, general aviation aircraft, a simpler version of the aileron system may be utilized to facilitate construction and minimize weight. The auxiliary flap panel may be left to function completely independently of the aileron panel. Its stowed position would be the neutral position, and it would move downwards only as a flap. The auxiliary flap panel would not accompany the aileron panel in its upward excursions.
The aileron system of the present invention is placed at the trailing edge of the wing in much the same location as a conventional aileron. However, the inventive aileron is deflected upwardly only. As with other ailerons, deflection results effectively in a change of the airfoil""s camber and thus a change in the lift coefficient, CL. In the case of the present invention, the upward deflection of the aileron results in a negative change in CL. The wing deploying the present aileron then produces less lift than the other wing with its inventive aileron maintained in the neutral position. Thus, the wing drops and the aircraft is rolled toward the lowered wing into a turn. The upwardly-deflected inventive aileron protrudes into the stream of air flowing over the wing, creating form drag, to rotate the nose of the aircraft toward the turn. Unlike activation of conventional ailerons, this action produces favorable yaw.
The present invention""s functional property of favorable yaw aids in both spin avoidance and spin recovery. For an airplane using the present aileron system, the same stick movement used by a pilot to roll right and out of the left hand spin described above, results in only the right aileron going up and on the outside of the spiral. The outward yawing motion plus the outside wing being depressed will roll the airplane away from the spiral center and aid in recovering from the spin. This will augment the opposite rudder input usually used for spin recovery. The form drag associated with the present invention also aids in spin recovery. Depending on the installation, this effect may be accentuated by the simultaneous deployment of the auxiliary flap panel with the aileron panel, creating a drag rudder on one wing, in this example the right wing.
Favorable yaw also ameliorates the difficulties associated with asymmetric loss of power during flight in multi-engine aircraft. The minimum controllable airspeed, Vmca, will decrease with use of the present invention, as will the required rudder authority and size, while aircraft performance will increase.
Since it deflects upwardly only, the aileron system of the present invention frees up the entire wing""s trailing edge for installation of high lift or drag devices to lower approach, landing and takeoff speeds. With lower approach and landing speeds, aircraft, particularly heavy commercial or high performance military aircraft, may gain access to shorter runways. Carrier-borne aircraft may have slower, safer approaches. These aircraft will have lower requirements for ground braking and the maintenance of such systems. Additionally, the invention may be deployed symmetrically on both wings for flight path control, or symmetrically in concert with flaps to function as air brakes or drag rudders.
The present invention is a simple system. It results in aircraft control systems and overall operations that are safer, more efficient and aerodynamically correct, simpler and more economical to produce and maintain. It lends itself to systems of lighter weight, with the weight savings being traded for increased fuel, cargo or passenger capacity, or simply a lighter-weight aircraft.
Other objects and features and additional advantages of the invention will be apparent from the foregoing and the following description and discussion, in conjunction with the accompanying drawings.